The present invention relates to a procedure and a device for the speed control of a closed gas turbine plant containing a working medium cycle, fitted with one or several by-pass valves serving as adjusting members for the working medium cycle, and using measuring transformers for measuring the working medium cycle high and low pressure as well as the actual speed and the nominal speed.
Procedures and devices like these are well known. With these gas turbine plants, the control behavior of the speed control can be improved by introducing to the regulator high and low pressure signals from the gas turbine cycle as auxiliary control values. The hitherto existing plants make use of this possibility in a way that the speed actual signal, the speed nominal signal and the pressure signals are combined in a summation member located before the regulator. The resulting signal is then conducted to a regulator whose behavior is essentially proportional-integral (PI-regulator) and whose exit acts on a by-pass valve serving as an adjusting member (see Bammert, K. and Key, G.: "Dynamic behaviour and control of single-shaft closed cycle gas turbines" = Dynamisches Verhalten und Regelung von einwelligen geschlossenen Gasturbinen, Journal of Engineering for Power, Transactions of the ASME, October 1971, pp.447-453).
As is well known, a PI-regulator changes its output value until the regulator input signal disappears. In case the regulator input signal is combined from several signals, a stationary balance condition (state of inertia) is obtained only when the sum of all regulator input values permanently disappear.
With a closed cycle gas turbine whose performance is controlled by by-passes, a performance modification results in a permanent modification of the high and low pressure. In case the signals of these pressures are supplied on a regulator, they result, after a performance modification in corresponding permanent regulator input signals. With the above described combination of speed and pressure signals, the regulator input value resulting therefrom in the state of inertia can therefor disappear only when the pressure signals are neutralized by a speed signal of a corresponding value. Thus the speed control as described above and being well known shows the disadvantage that a load modification always means a permanent perturbation of the speed as to its nominal value. The result of this is the fact that, with hitherto existing closed cycle gas turbines, the speed, i.e. its nominal value, had to be adjusted by hand until the nominal speed had been restored.
Thus the problem is to find a procedure and a device by which the above described disadvantages could be avoided, and this in a way that, as a final result, the speed is adjusted anew to its nominal value.